As a federal prosecutor and judge, we saw that these policies do not work.

Last week, Attorney General Jeff Sessions instructedthe nation’s 2,300 federal prosecutors to pursue the most serious charges in all but exceptional cases. Rescinding a 2013 policy that sought to avoid mandatory minimums for low-level, nonviolent drug offenders, Sessions wrote it was the “moral and just” thing to do.

Sessions couldn’t be more wrong. We served as a federal prosecutor and a federal judge respectively. In our experience, mandatory minimums have swelled the federal prison population and led to scandalous racial disparities. They have caused untold misery at great expense. And they have not made us safer.

Mandatory federal drug sentencing is unforgiving. A person with one prior drug felony who is charged with possession of 10 grams of LSD, 50 grams of methamphetamine, or 280 grams of crack cocaine with intent to distribute faces 20 years to life. With two priors — no matter how long ago they occurred — the penalty is life without parole. As one federal judge has written, these are sentences that “no one — not even the prosecutors themselves — thinks are appropriate.”

They waste human potential. They harm the 5 million children who have or have had a parent in prison — including one in nine black children. And they wreak economic devastation on poor communities. Studies have found, for example, that formerly incarcerated employees make 10 to 40 percent less money than similar workers with no history of incarceration and that the probability of a family being in poverty increases by almost 40 percent when a father is imprisoned.

Still, in 2003 then-Attorney General John Ashcroft pushed line prosecutors to charge mandatory minimums whenever possible. His policy helped grow the federal prison population from 172,000 to nearly 220,000 over the next 10 years. This was part of a wider national trend that grew the country’s incarcerated population to 2.2 million, almost 60 percent of them black and Latino.

In 2013, Attorney General Eric Holder recognized that this system of mass incarceration was at odds with the Justice Department’s values. He told attorneys to reserve the most severe penalties for the most serious offenses. That meant charging cases in a way that would not trigger mandatory minimums for a specific group of defendants: nonviolent, low-level drug offenders, with no ties to gangs or cartels, no involvement in trafficking to minors, and no significant criminal history.

Holder’s policy was part of an emerging criminal justice reform movement. Since 2009, more than half the states have passed legislation to relax mandatory minimums and restore judicial discretion — including deep-red Georgia, Louisiana, Mississippi, Oklahoma, and South Carolina. A new crop of prosecutors is openly questioning the use of long prison terms for minor drug crimes. And a bill to ease federal sentencing has bipartisan support in Congress.

Sessions is bent on reversing this progress.

It would be one thing if Holder’s reform efforts had failed — but they did not. The federal prison population fell for the first time after 40 years of exponential growth. It is down 14 percent over the past 3½ years. While we need a wider conversation about how we sentence all offenders, including violent offenders, state and federal, this was a start. The 2013 policy sent a message about the need to be smart, not just tough, on crime, and the role of prosecutors in that effort.

Sessions’s assault on the past few years of progress might also make sense if mandatory minimums for minor drug offenses were necessary to combat crime — but they are not. A 2014 study by the U.S. Sentencing Commission found that defendants released early (based on sentencing changes not related to mandatory minimums) were not more likely to reoffend than prisoners who served their whole sentences. That is, for drug charges, shorter sentences don’t compromise public safety. Indeed, research shows it is the certainty of punishment — not the severity — that deters crime.

Sessions’s fixation on mandatory minimums might also be more palatable if they were cost-effective — but they are not. Federal prison costs have ballooned to $7 billion, more than a quarter of DOJ’s budget, driven by a population that is nearly half drug offenders. And yet as detailed by the conservative American Legislative Exchange Council last year, most experts believe that expending public resources to incarcerate these offenders is profoundly inefficient.

Sessions’s defenders will say his policy only requires prosecutors to charge the defendant’s true conduct and apply the statutes Congress enacted. But floor statements from legislators show that Congress intended these mandatory minimums to be used against “kingpins” and “middle-level dealers,” not the minor offenders to whom they have been applied.

One of us served as a federal prosecutor under Holder and had mandatory minimum charges at his disposal. The message from the top downwas that prosecutors were to pursue justice. Winning did not mean getting the longest sentence possible. It meant getting the right sentence, one that fit the crime and that respected the interests of victims, defendants, and the public.

The other of us served as a federal judge for 17 years, including during the heyday of the Ashcroft regime. She believes that roughly 80 percent of the sentences she was obliged to impose were unjust, unfair and disproportionate. Mandatory penalties meant that she couldn’t individualize punishment for the first-time drug offender, or the addict, or the woman whose boyfriend coerced her into the drug trade.

Under Sessions, prosecutors will be required almost always to charge mandatory minimums, however unjust. They will bind judges’ hands even when the facts cry out for more measured punishment. The result will be great suffering. And there is no good reason for it.

Nancy GertnerNancy Gertner was a federal district judge in Boston from 1994 to 2011, has taught sentencing law for 19 years, and is a professor at Harvard Law School. Follow

Chiraag BainsChiraag Bains was a prosecutor and senior counsel in the Justice Department’s Civil Rights Division from 2010 to 2017 and is a fellow at Harvard Law School. Follow